Functional laminates also refer to semi-finished products like prelaminates or inlays, which are used for example for the manufacturing of smart cards equipped with chips or chip modules, RFID antennae and the like. They usually consist of a number of core layers and two or more cover layers covering the core layers, wherein the chip module is embedded in the layers. The layers usually consist of a plastic material such as polycarbonate or polyethylene terephthalate.
In DE 197 10 656 A1 a smart card is disclosed, wherein layers have recesses to accommodate components such as an antenna coil or a chip module or another semiconductor. The component is embedded with a filler in the stamped-out region. The filler is initially in fluid form. Excess filler is removed and the layers are laminated under heat and pressure.
In WO2007/089140 A1 an identity document is disclosed, consisting of a support and a chip accommodated therein. The support may be produced by laminating different layers, one or more of these layers being provided with an opening for accommodating the chip. Laminating or applying the plastic in another way takes place at a relatively high temperature. During cooling, the support and the chip exhibit different shrinking properties, resulting in stresses which may lead to cracks. It is proposed to provide an auxiliary layer between the layer directly adjoining the chip and the subsequent layer. This auxiliary layer consists of a rubber-like material having a thermal coefficient of expansion which is greater than that of the adjoining two layers.
In EP 1 502 765 A1 a method for producing a booklet, in particular an identity booklet is disclosed. The booklet comprises a cover, several leaves and at least one data page with a flexible layer. The layer is provided with means which further strengthen its joint with a data carrier. Such means may be recesses, in particular.
When the layers are laminated using heat and/or pressure the macromolecules of the plastic material tend to shorten thus causing the plastic material to shrink. Since the chip module itself does not shrink the material is subjected to mechanical stress eventually leading to deforming, cracking or delaminating the material thus limiting the service life of the smart card.